In the field of copper wire communication cables, the copper wires are arranged in pairs. Although a single pair may stand alone, it is common for copper wire pairs to be bundled into multiple pairs within a single outer jacket. Although any number of pairs may be contained within a single jacket, a particularly common arrangement is to include four pairs within a jacket.
A common problem in unshielded copper wire cables (containing only twisted pairs of insulated copper wire without any metal shielding) is crosstalk which generally refers to communication signal interference that occurs between signals traveling along two different adjacent or near by copper wire pairs. To address this, the copper wire pairs are twisted around one another at a particular rate, forming a twisted pair, so as reduce crosstalk between the pairs. The twisting of the copper wire pairs reduces the instances that a first pair of wires runs in parallel to a second pair of wires, thus reducing crosstalk between the pairs. The rate of twisting in the pairs results in a particular lay length referring to the longitudinal length along which one full twist of the copper wires occurs.
In prior art arrangements where four twisted pairs are included in one jacket it is common to use four different lay lengths, one for each of the four twisted pairs. These varied rates of twisting results in a reduced number of incidences where the wires in the pairs run parallel to one another, affecting a reduction in crosstalk. For example, in a typical four pair cable, arranged in a compact square/rectangle, there are six different crosstalk combinations that need to be addressed, as shown in prior art FIG. 1 (labeled C1-C6).
It is typically known that the shorter the lay length of a particular pair in a multi-pair cable, the more crosstalk is reduced. However, shorter lay lengths obviously use more wire per length of cable, and thus there are limitations on how short the lay length can be in any given copper wire twisted pair. Therefore, it is ideal to have the longest lay length possible that meets the desired crosstalk threshold.
In addition to the crosstalk that occurs between pairs within the same cable, an additional type of interference occurs between twisted pairs in adjacent cables referred to as ALIEN crosstalk. Although crosstalk within a jacket is easier to manage because the lay lengths of the closest pairs can be tightly managed, ALIEN crosstalk is harder to predict and mitigate, since external cable conditions (the number of adjacent cables, having the exact same twist rate from cable to cable, the distance between adjacent cables, longer pair lay length in adjacent cables, unknown lay lengths of twisted pairs in adjacent cables, etc. . . . ) can not be easily predicted.
One prior art method for preventing such ALIEN crosstalk is to provide shielding for the cable jacket. However, this shielding is not always feasible as it adds significant costs, installation time and weight to the cable. Another manner for providing protection against ALIEN crosstalk is to provide a gap between the pairs and the inside diameter of the jacket by placing a helical filament around the pairs within the cable. The gap produces a greater physical distance between the pairs of a first cable and the pairs of an adjacent cable, but the filament adds complexity to the production process and furthermore results in significantly larger cable diameter (0.350″ when applied to a typical four twisted pair cable).
Thus, the problem of ALIEN crosstalk between twisted pairs in adjacent cables still persists, yet the prior art solutions have proven to be inadequate for smaller cable diameters.